I was doing this following these steps as mentioned in the link.
IInAppBillingService.aidl file to your Android project.
(1) If you are
The structure that @David mentioned works fine in Android Studio 1.2.
Your path for the billing folder should look like:
[YOUR_APP_FOLDER]/app/src/main/aidl/com/android/vending/billing/IInAppBillingService.aidl
This is where you can check the IInAppBillingService.java generated file:
[YOUR_APP_FOLDER]/app/build/generated/source/aidl/debug/com/android/vending/IInAppBillingService.java
Good luck !